I brewed my second batch this last weekend. The bubble action of this batch is totally different from the first batch. The first batch had an OG of 1.071 and used Safale-04 yeast. This batch bubbled vigorously and for only a few days. The second had an OG of 1.052 and used Nottingham yeast. This second batch hasn't bubbled as vigorously but is still going at it. Is this because of the yeast, because they have different OGs, or because it was sunny this weekend and snowing the first weekend?

That's funny. Just before i saw your headline, I was looking at my fermenter (3rd batch) bubbling away wondering why the action was so different the batch before. The batch before was the exact same recipe except the yeast. I used dry yeast before (don't remember what kind) and it seemed to be quite done after just three days (no foam on top, specific gravity stabilized). This time I used a test tube yeast (WLP 008). After 4 days my airlock is still quite active. I can't wait to taste the difference between the 2.

Yeast is a living thing so every fermentation will be different. As for reasons why you have named a few. Different yeast strains, different OG, temperature, aeration, pitch rate, amo0unt of nutrients in the wort, etc. will all have an effect on how vigorous and long the fermentation will be.

Every fermentation will be different. In your case the most obvious difference is the OG. There was a ton more sugar in your first brew so the yeast have a lot more to eat so one would expect the fermentation to be more vigorous. I'm in the middle of making a beer that had an OG of ~1.075 using WhiteLabs Burton Ale yeast, it was bubbling continuously for two and a half days, it's now been 5 days and it's slowed to a bubble every 15 seconds or so and the krauzen still hasn't fallen. Compared to previous brews that would bubble every 5 seconds at max and the krauzen formed and fell within a couple days.